I would like to modify the boot loader settings and tried to open the file grub.conf
However, it is said that the file could not be opened, as seen in the attachment.
Tried to authenticate as 'root' before opening the file, but the problem still exist...

Pardon, what is 'su-'?
I tried typing the line [gedit /boot/grub/grub.conf] in the terminal but the sole effect is exactly the same as double clicking the grub.conf file: could not open the file /boot/grub/grub.conf

Hello
su - (note space) gives you super user (root) status to the whole system, su on it's own gives root privileges only to the directory you're in when you opened the terminal.
Be careful with grub.conf btw, so to open it type

Code:

su -

then press enter, password: will then come up, type your root password, nothing will be displayed as you type, then enter again, then

su - (note space) gives you super user (root) status to the whole system, su on it's own gives root privileges only to the directory you're in when you opened the terminal.

Wrong. I've often used su to become root, then changed from one directory to another without losing root access. When you use su by itself, you change your userid to zero, giving you root privileges. When you use su - you LOG IN AS ROOT, giving you root's environment (including PATH) and changing the working directory to /root.

Wrong. I've often used su to become root, then changed from one directory to another without losing root access. When you use su by itself, you change your userid to zero, giving you root privileges. When you use su - you LOG IN AS ROOT, giving you root's environment (including PATH) and changing the working directory to /root.

my apologies, I could have perhaps worded my reply better, I too switch from one directory to another while using su by it's self, noting the op's understanding of linux I didn't want to complicate matters.
There's a fine line between sounding patronising and big headed as it's difficult to know the level of competence of a poster, I mean I would say I had a high level of competence with some things linux and zero understanding of others